A locking device to which the present invention is directed has been disclosed, for example, in the below-listed patent documents 1 to 5. The locking device principally comprises a pole, a lock base that can slide along the pole, a lock hole provided in the pole, a lock pin provided movably to a lock base in the longitudinal direction of the lock pin, thus enabling the lock pin to engage the lock hole in a locking position and also to disengage the lock hole in an unlocking position, an elastic body to push the lock pin mounted on the lock base toward the locking position all the time, and an operating lever provided on the lock base to move the lock pin to the unlocking position. With such a device, a relative hoisting/lowering motion of the pole and the lock base is prevented after the lock hole and lock pin come into alignment by a relative hoisting/lowering of the pole and the lock base, because the lock pin enters the lock hole with the help of an elastic body to place the locking pin in the locking position. From such a state, when the operating lever pushes against the elastic body, the lock pin moves out of the lock hole and is placed in the unlocking position; thus, a relative hoisting/lowering of the pole and the lock base is permitted.
Patent Document 1 Japanese Utility Model Registration No. 2504766
Patent Document 2 Japanese Unexamined Patent Application No. 8-9938
Patent Document 3 Japanese Unexamined Patent Application No. 10-88949
Patent Document 4 Japanese Utility Model Registration No. 3123507
Patent Document 5 Japanese Utility Model Registration No. 3133263